Control mechanism for regulating flow of fluid pressure in hydraulic systems



Aug. 26, 1947. B. JAPIKSE 2,426,509

CONTROL MECHANISM FOR REGULATING FLOW OF FLUID PRESSURE IN HYDRAULIC SYSTEMS Filed March 20, 1943 2 Sheets-Sheet l i I l 7 TI I Q 7 Q' Aug. 26, 1947. B. JAPIKSE 2,426,509

CONTROL MECHANISM FOR REGULATING FLOW OF FLUID PRESSURE IN HYDRAULIC SYSTEMS Filed March 20, 1943 2 Sheets-Sheet 2 19 v 4 J1 27 4a 1a 7:;

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4 '1 5 a2 5 I 53- Z 7 4&5 5 6 I i I'TI z-+ I 4 Patented Aug. 26, 1947 CONTROL MECHANISM FOR REGULATING FLOW OF FLUID PRESSURE. IN HYDRAU LIC SYSTEMS Bertrand J apikse, Reiflton, Pa., assignor to Birdse boro Steel Foundry & Machine 00., Birdsboro, Pa., a corporation of Pennsylvania Application March 20, 1943,, Serial No. 479,934

6 Claims. 1

The invention pertains to a hydraulic power press control and more particularly to a servo linkage control mechanism for determining the flow of fluid pressure from a pump in the hydraulic system of the power press.

An object of the invention i the provision of a servo linkage control means for regulating the flow of fluid pressure from a pump of a hydraulic power'press' to eifect a complete automatic cycle of the press.

A feature of the invention is the provision, in a servo linkage control mechanism, of a lifting means for raising linkage means to a predeter-- mined position and electrically controlled means arranged to retain the linkage means in a raised position while the lifting means is in the process of returning to normal position.

Another feature of the invention is the provision, in a servo linkage control mechanism, of an electrically responsive means arranged to be contacted by linkage means during a lifting action of the latter to result in the actuation of a linkage arresting means for retaining the linkage means in a fixed elevated position and at the same time causing a removal of forces which actuate a lifting means so that the latter can return to normal position during the last stages of a pressing operation and permit a more rapid reversal action of a movable platen during its pressing cycle.

A still further feature of the invention is to provide, in a hydraulic power press control, a fluid responsive means for moving a linkage means to determine the flow of fluid from a pump and having a notched means and displaceable or shiftable means arranged to be contacted by a selectively controlled means for determining the position or disposition of linkage means.

The above as well as numerous other objects and features of the invention will become appar- .ent by referring to the succeeding description considered together with the accompanying drawings which disclose an exemplified form of the invention and wherein:

Figure 1 is av side elevational View of the hydraulic power press control mechanism embodying the present invention.

Figure 2 is, a plan view of the hydraulic power press control mechanism illustrated in Figure 1.

Figure 3 is an end elevational view of the structure disclosed in Figure 1.

Figure 4 is a vertical cross sectional View taken along the line l4 of Figure 2, looking in the direction of the arrows.

Figure 5 is a vertical cross sectional view taken 2.- along the line 55 of Figure. 2, looking in the directionof the arrows.

Figure 6: is a horizontal cross sectional view taken along the line. 6-45 of Figure. 1,. looking in the direction of the. arrows.

Referring now in detail tothe drawingswherein like reference characters designate like parts, the numeral I indicates in a. general manner a servo linkage: control mechanism adapted to control or regulate the action of a movable platen 2 oia hydraulic power press (not shown) in that the mechanism is arranged to. control the flow of'fl-uid pressure from a pump (not shown) in the hydraulic system of a power press. For a general description of a hydraulic power press in which the present invention is incorporated, reference is hereby made. to my copending application entitled Hydraulic power press which bears Serial Number 473552 1, and was filed January 25., 1943. The pump. above referred to, under the. action of the servo linkage. control mechanism is. adapted to direct fluid' pressure to pullback cylinders (not shown). to cause an upward movement of a movable platen or direct fluid pressure to a main cylinder (not shown) of the. power press to cause a downward or pressing action of the movable platen. It is, of course, to be understood that considered general-1y, when the servo linkage control mechanism is. disposed at normal position hereinafter set. forth in detail, neither the pullback cylinders nor main cylinder are being serviced by the pump and, accordingly, the movable platen is retained in elevated position.

The servo linkage control comprises a support plate 3 mounted on any convenient portion of the hydraulic power press, such as a suction tank 4 illustrated diagrammatically in several views of the drawings. Surmounting the support plate is a cylinder 5 having a base 6 removably secured to the support plate by means of cap screws 1' or any other desirable means. Upstanding vertically from the base is a cylinder body or barrel 8 firmly secured to the base by means of welds and having extending partially therethrough an axial bore 9, the upper extremity of which is desirably enlarged to accommodate a gland I0 which is retained firmly in fixed position by means of rotatable means or cap screws I I which project through a horizontally disposed flange I2 of the gland and into the body of the cylinder. In subjacent relation to the gland within the enlarged portion of the bore are a series of pressure or packing rings I3 which are held against the gland by means of a throat bushing I4 occupying the lower area of the enlarged portion of the bore.

As will be noted, the gland, packing rings and throat bushing form a restricted opening into the cylinder bore. Disposed within the cylinder bore is a plunger I having a lower extremity 15a neatly fitting the bore while the upper extremity I5!) is closely fitted by the gland, packing rings and bushing to prevent leakage of fluid therebetween. Secured to the one side of the cylinder barrel or otherwise associated with the mechanism is a three-way solenoid operated valve it of a commercially available type which derives its fluid supply through the pipe I! (see Figure 3) communicating with any source of supply such as the pump above referred to. The valve I6 is in communication with the bottom or lower area of the cylinder bore through the port l8 so as to subject the lower -exposed area of the piston to fluid pressure and urge it outwardly or upwardly of the cylinder. Generally considered, without dwelling elaborately on the electrical circuit or hook-up of the press which forms no part of the present invention, when an operator depresses a start button (not shown) in the electrical circuit of the press this action will, through suitable relays, energize the solenoid of valve l6 to permit the admission of fluid to the interior of the cylinder through the port l8.

Extending transversely of the linkage operating mechanism is a piston crosshead l9 secured to the upper free extremity of the piston through the medium of a cap screw l9a and extending outwardly beyond the limits of the cylinder barrel to have adjacent the ends thereof suitable apertures. Positioned on each side of the cylinder body in spaced relation thereto are a plurality of pull rods 29, vertically disposed and having their upper extremities extending through the aligned or accommodating apertures of the crosshead to have rotatable means or nuts 20a threadedly related thereto so that any upward action of the crosshead will be reflected in the pull rods. Vertically disposed and transversely extending guide lugs 8a are formed integral with the cylinder body to receive the pull rods and retain them in a fixed predetermined path. Each pull rod has, adjacent its lower extremity, a nut 29b positioned a given distance below an associated guide lug 8a to limit or determine the entire permissible range of movement of the pull rods. Associated with each pull rod intermediate the ends thereof as well as intermediate the related guide lugs is a collar 2| removably secured to the related pull rod by a pin Zia so as to be arranged to move with the pull rod.

Extending normally to the direction of the guide lugs is a hub 22 formed integrally with or otherwise fixedly secured to the cylinder barrel intermediate the height thereof. The hub has a suitably lined bore for the accommodation of a shaft 23 which, while freely rotatable Within the bore is, however, prevented from shifting laterally of the hub by means of the bearinglinings 23a. Keyed to the shaft so as to be movable therewith is a lever 24 extending horizontally beyond the limits of the cylinder in spaced relation thereto and having intermediate its ends a clip 25, U-shaped in configuration when considered in plan. The clip formed integrally with or secured to the lever straddles an associated pull rod 20 and has an under surface 25a cylindrical in configuration to thereby present a smooth surface against which the subjacent collar may abut, as will be hereinafter explained. Positioned at the opposite end of the shaft from the lever 24 and on the other side Of t e hub from the lever 2 3 is an auxiliary lever 25 which is also keyed to the shaft. The auxiliary lever has its free extremity bifurcated as at 2611 to straddle the aligned and associated pull rod and overlie the related collar. The bifurcated end of the auxiliary lever also has a cylindrical lower surface 261) which is in horizontal alignment with the cylindrical surface of the lever clip and so as to present a smooth surface for the collar to abut. Also keyed to the shaft outwardly of and adjacent to the lever 24 is an operating arm 2'! vertically disposed and having its upper free extremity pin connected to link 28 which extends horizontally from the operating arm to be pivotally connected to a pump which may, through the action of the link, be arranged to direct fluid pressure to the pull back cylinders of the press or, if desired, to the main cylinder of the press as well as be arranged to service neither the pullback cylinders nor main cylinder as is the case when the movable platen is in elevated position preparatory to commencing a pressing cycle. This latter condition exists when the elements of the servo linkage operating mechanism are in the respective positions illustrated in the drawings. As will be noted from the above, when the solenoid operated valve is energized, fluid pressure is permitted to enter the lower area of the cylinder bore to urge the piston outwardly of the cylinder, which action will be reflected in the pull rods. Such action will then cause the pull rod collars to contact the surfaces 25a and 26b to result in the lever and auxiliary lever being urged counterclockwise and impart a like action to the shaft and operating arm so as to position the operating arm in the location indicated in diagrammatic lines and designated by the character 29. With the operating lever in this position the link has been displaced to the left from normal position and the pump has been set to cause a flow of fluid to the main cylinder of the press to thereby urge the movable platen downwardly in what might be considered the first part of the pressing operation or cycle.

Because Of the fact that the return of any hydraulic piston is of necessity due to its characteristics generally at a limited speed because it is necessary to force fluid out of the cylinder, means has been incorporated in the servo linkage control or operating mechanism to eliminate this lapse or delay and thereby obtain a much more rapid or sensitive press reversal so as to obtain or eifect a higher production on the press. If it were necessary to wait until the fluid were forced out of the cylinder then the movable platen could not be started toward its raised position until after a relatively long lapse of time required to exhaust the cylinder which would hamper or delay the completion of the pressing cycle. So as to permit the piston and its associated lever actuating elements to return to normal or lower position while at the same time retaining the operating arm thrown over to the left as indicated at 29 during the closing action of the movable platen or pressing operation, there is provided a hanger or connecting bar 30 having a clevis or jaw type upper extremity 3| overlapping and pin connected to a related or free extremity of the lever 24. The hanger is Vertically disposed and extends from the lever downwardly beyond the horizontal plane of the support plate for an appreciable distance where it terminates in a preferably integrally formed horizontally disposed U-shaped semi-annular member or stirrup 32.

Depending from the support plate in advance and to the one side of the cylinder is a pair of guide bolts 33 having in sliding relation therewith a cross-head or bridge 34 which is provided with oppositely disposed journals 35. Mounted upon the journals are a plurality of needle bearings 36 arranged to neatly fit into suitable and aligned apertures 32a, of the stirrup to be held in place by cover plates 31 which are secured to the stirrup by means of cap screws 31a. As will be noted, the stirrup by being journaled to the bridge at two'spaced points will, during service, not subject the bridge to a tilting or binding action and, accordingly, will allow the bridge to be moved freely along the guide bolts in a vertical direction.

The bridge is provided with a centrally disposed opening 38 extending vertically therethrough and which accommodates a stem 39 of a thimble 40* disposed intermediate the guide bolts. Engaging an upper extremity of the thimble is a screwed on collar 4| which bears upon the bridge to prevent relative movement between the thimble and bridge in one direction. Shifting between these two members in the opposite direction is prevented by means of a shoulder 4l-a which bisects the stem 39 and is in subjacent'relation to the bridge. Accordingly, it will be noted that while the thimble cannot move vertically relative to the bridge it is, however, arranged to rotate freely within the bridge. Threadedly associated with and upstanding from the thimble is an adjusting screw- 42 which extends vertically through the plane of the support plate. This screw is furthermore locked to the thimble by means of locking pin 42a. Disposed upon the support plate and retained in a fixed predetermined position by means of holding nuts of the guide bolts 33 is a guiding sleeve 43 generally tubular in formation and, accordingly, presenting a vertically extending opening 44 which is lined with a suitable bushing 44a. Arranged to move vertically within the guiding sleeve bushing is an adjusting sleeve 45 having its lower extremity provided with a cross arm 46 which is slidably associated with the guide bolts to thereby retain the adjusting sleeve in a predetermined path during service movements thereof as well as prevent a rotary motion of the adjusting sleeve. The adjusting sleeve is of hollow construction and provided with interior threads adjacent its lower extremity which are rotatably associated or interlocked with exterior threads of the adjusting screw so that in operation of the press adjustments may be made for a. reason to be hereinafter set forth. For the present it is sulficient to state that any action in the hanger will, through the intermediate elements hereinbefore described, be reflected in thev adjusting sleeve in that when the hanger is elevated in response to a counter-clockwise movement of the lever, the adjusting sleeve will be elevated through a corresponding range of movement.

The guiding sleeve is provided with a boss 41 disposed a slight distance above the plane of the support plate and into which is screwed an axle or pivot pin 48 extending horizontally and inwardly or laterally of the mechanism. Journaled on the pivot pin is a dog lever or latch 49 comprising a pivot pin engaging hub 50 having upstanding therefrom a leg 59a which terminates in a horizontally and laterally directed lip 50b stationed in the area above the upper extremity of the guiding sleeve during certain movements of the dog lever. Projecting from one side of the latch hub is a horizontally disposed leg 500 which extends beyond the extended transverse plane of the cylinder where it merges into a lateral branch 5001. The branch in the area of the longitudinal vertical plane of the cylinder terminates in a rearwardly and upwardly extending extremity 506 which is pivotally connected to a dog lever or latch operating solenoid 51. This last mentioned solenoid 'is mounted on the uderneath portion of the cylinder hub 22 to be removably secured thereto.

When the operator depresses the start button (not shown) in the electrical circuit he will, through contain relays (not shown) deenergize latch solenoid 5|. As previously stated, this same action will energize the valve solenoid to cause a counterclockwise rotative action of the levers and lifting action of the hanger which will be reflected in the adjusting sleeve bein urged vertically and upwardly through the guiding sleeve. This. equence will, as previously stated; start the operating arm toward the position indicated as at 29 and cause a downward motion of the movable platen. As soon as the link approaches its highest preset position the cross arm 46 will contact a dependin limit switch pin 52 carrying it upwardly therewith. The pin 52 is povotally connected to a limit switch 53 which is mounted upon a suitable bracket 53a anchored to the support plate so that the last portion of the linkage travel will open the circuit of the limit switch, thus deenergizing the solenoid of the three-way valve l6 whereupon the pressure beneath the operating piston will be exhausted. The upper or annular area of the piston has, all the while, been maintained under constant pressure through pipe connection Ila and this downward pressure will therefore force the piston down. When, however, the solenoid of the threeway valve is deenergized the latch solenoid is energized and ill, is to be remembered that the leverage mechanism is also at this time elevated to its highest preset position. By energizing the latch solenoid the latch will be actuated inv a clockwise direction to cause the latch lip 50b to enter an accommodating or suitable notch 54 in the adjusting sleeve. By this arrangement, therefore, the linkage, by reason of the interlock between the latch lip and adjusting sleeve, will be retained in an elevated position while the linkage actuating mechanism which includes the piston and pull rods has been returned to their normal retracted or lowermost position.

After the platen of the press has descended upon the work and pressure has been built up in the main or pressing cylinder a pressure responsive device (not shown) causes a limit switch (not shown) to be tripped which again deenergizes the solenoid 5|. This action of the solenoid 5;! will be reflected as a counterclockwise movement of the latch to withdraw the latch lip from the engageinotch. As soon as this takes place the means for retaining the linkage in elevated position is disconnected and the linkage immediately and rapidly drops or descends by gravity to its lowermost position because during this lapse of time the pressure beneath the operating piston has been completely exhausted. This action, therefore, will cause the operating arm to move from the position indicated diagrammatically as at 29 in a clockwise direction to a position also indicated diagrammatically as at 55. When, therefore, the operating arm reaches this latter mentioned position the pump will be actuated to cause the release of pressure from the main cylinder and to cause the flow of fluid to the pullback cylinders and result in a raising action of the movable platen.

When the linkage is dropped rapidly by the releasing of the latch it will, of course, accelerate substantially at a rate of speed determined by gravity and would cause a sharp metallic impact when the linkage reaches its lowermost position. To cushion the last part of the downward travel of the linkage, there has been provided a dash pot 58 having a housing 51 secured to the one side of the cylinder and opening outwardl or longitudinally of the linkage mechanism. Within the housing is an air cylinder 58 in which operates an air plunger 59 with piston ring 59a. This air plunger is forced outwardly by means of an enclosed compression or helical spring 60. The outward travel of the air plunger is limited by means of a retaining plate 6| disposed across the opening of the housing and fastened thereto by means of screws Ela. This retaining plate is provided with air vent holes at Bib. Arranged to strike against the air plunger of the dash pot is a bar 62 extendin radially from and formed rigidly with the lever 24 so as to be rendered movable therewith. The bar has a transversely extending finger, striking arm or anvil 63 normally spaced from and arranged to move in an arcuate path about the shaft so as to contact or be intercepted by the air plunger of the dash pot. When the dropping linkage approaches the end of its downward travel, the finger, moving with the linkage strikes the air plunger and forces this plunger inwardly of the dash pot thereby building up an increased air pressure within the dash pot. This air will then breathe out between the clearances of the air plunger piston ring and housing to regulate and limit the rate of speed with which the linkage reaches its lowermost position or comes to rest. A check valve 51a is provided to permit air to fiow into the cylinder space when the spring returns the dashpot plunger outwardly. This check valve comprises a ball 51?) which is seated upon a seating area 51c of orifice plug 51d. A light spring 51c holds the ballnormally against its seat but is of light enough construction to permit atmospheric pressure to open the valve when the spring urges the plunger outwardly. If the leakage of air through the seal of piston ring 59a is insuifioient to properl regulate the expulsion of air during the cushionin stroke of the dashpot plunger, it may further be controlled by providing a supplementary orifice as shown in dotted lines at 591 and the size of this orifice may be selected to suit requirements.

On the other hand, if the cushioning action must be made more effective it can be accomplished by reducing the air space within the cylinder and plunger confines. This can be accomplished by inserting a solid filler plug 599 inside of the spring. Cushioning can further be improved by reducing the leakage through the clearances of the sealing joint of the piston ring.

The structure of the present invention is further provided with a means whereby a downward speed of the movable platen may be adjusted as will be the case where the pump is placed on only a part stroke forward when the movable platen will travel at a proportional speed. For the accomplishment of this purpose it will be noted, as hereinbefore described, that the adjusting sleeve 45 has been provided with the adjusting screw 42, the latter of which can rotate but must, due to the collar 4| and the shoulder 41a,

at all times move either up or down with the bridge. Pivotally secured to the lower free extremity of the thimble is a universal joint 64 into which is extended a connecting rod 65 with a jamb nut 65a. arranged to prevent, after a presetting, a relative rotative movement between the connecting rod and universal joint. Associated with the lower end of the connecting rod is a clevis 66 in vertical alignment with the connecting rod and retained in assembled relation therewith by means of a swivel screw 61 which extends through the clevis and into collar 651) which forms the lower part of the connecting rod. As will be noted, the connecting rod and universal joint may rotate about a common axis as a unit while the clevis is held from movement by crank 68 and by so doing the adjusting sleeve may, by manipulating the collar 651), be raised or lowered from illustrated position to thereby alter or change the distance between the adjusting sleeve and bridge. Accordingly, when the distance between the sleeve and bridge has been increased the distance between the cross arm 46 and the adjacent extremity of the limit switch pin 52 has been decreased so that the operating arm 21 will complete only a portion of its capable movement before the limit switch 53 will be tripped and the latch operating solenoid will be energized to position the latch lip in the adjusting sleeve notch. At this time, therefore, the pump has been placed on only a part stroke to effect a slower downward movement of the movable platen. In like manner when the connecting rod is rotated in the opposite direction the distance between the limit switch pin 52 and cross arm 46 has been increased to effect a longer stroke of the operating arm and, accordingly, accelerate the action of the movable platen.

Pivotally connected to the clevis 65 is an extremity of an actuating arm 68 which extends a slight distance beyond the clevis so that during the reverse action of the movable platen, that is, when it is beingraised after a pressing operation, a lug 69 projecting horizontally or outwardly of the movable platen and disposed to move in a path to be intercepted by the actuating arm 68', may contact the latter and raise the linkage to normal position, such as is illustrated in the drawings when the operating arm 21 is vertical and the pump of the press is still pumping merely sufficient fluid into the hydraulic system of the press to overcome losses due to slippage but not sufficient to allow any movement of the movable platen.

Arranged on top of the adjusting screw out of the confines but Within the extended vertical limits of the guiding sleeve is a displaceable collar in bearing upon a shoulder H formed on the adjusting screw. The displaceable collar has a tapered or frusto-conical opening 12 slightly larger than the occupying portion of the adjusting stem so as to render the collar shiftable transversely of and relative to the adjusting screw. Bearing freely upon the collar is a washer 13 forming a footin for a compression or coil spring 14 held under compression by means of a washer and nut 15. Accordingly, when a selector switch (not shown) in the electrical circuit is opened, the entire electrical control circuit is deenergized and since during this time the latch closing solenoid 5| is deenergized and the latch lip is out of the path of the shiftable collar, the linkage may be operated manually through the actuating arm 68. When, however, the selector switch is closed the circuit is energized thereby energizing the latch operator may judge the neutral position of thelinkage and thus permitting starting of the press motor when the load on the pump is minimum, thereby reducing the load on the motor at this time and also further safeguarding the pump during its starting period.

If the collar were positioned above the latch at the time the latch solenoid is energized, for instance because the operator might have manipulated the actuating arm to cause such a relationship before turning the selector switch, and he should subsequently pull the linkage back, the collar is so constructed, as previously described, to work out of position to sufliciently clear the latch. When the selector switch is turned to the on position the press can be operated on an automatic cycle inasmuch as the latch prevents moving the linkage by hand beyond normal position or far enough to start the moving platen of the press on its downward travel.

From the above it will be noted that various changes and alterations may be made to the illustrated and described construction and relationship of parts without departin from within the spirit of the invention and scope of the appended claims.

Iclaim:

1. In a control mechanism, the combination of, fluid responsive means, linkage means for controlling a flow of fluid, said linkage means being arranged to be contacted and moved by said fluid responsive means after a predetermined travel thereof, means connected to said linkage means, said last named means comprising a notched means and a shiftable means, and a selectively controlled latch means arranged to engage said notched means or said shiftable means to thereby determine the position of said linkage means.

2. In a control mechanism, the combination of, fluid responsive means, linkage means for controlling a flow of fluid, said linkage means being arranged to be contacted and moved by said fluid responsive means, means carried by said linkage means, latch means arranged to contact said means for holding said linkage means in a-predetermined position after the movement thereof by said fluid responsive means, and shiftable means associated with said carried means and being arranged to pass said latch means in one direction only.

3. In a control mechanism, the combination of, a fluid responsive cylinder, reciprocating means .associated with said cylinder, linkage means arranged to be moved in only one direction by said reciprocating means, means carried by said linkage means, a selectively controlled latch arranged to contact said carried means for maintaining said linkage means in a predetermined position, and means adapted to be engaged by said linkage means upon nearing the limit of its travel in one direction for causing the drainage of fluid pressure from said cylinder and permitting the reciprocating means to return to its normal position.

4. In a control mechanism, the combination of,

a fluid responsive cylinder, movable means associated with said cylinder, pivotally connectedmeans arranged to be moved in one direction by said movable means, an arm rigid with said pivotally connected means, means carried by said pivotally connected means, latch means arranged to contact said carried means for maintaining said pivotally connected means in a predetermined position, means adapted to be engaged by said pivotally connected means upon nearing the limit of its travel in one direction for causing the drainage of fluid pressure from said cylinder and permitting the movable means to return to its normal position, means for disengaging said latch means from said carried means and permitting said pivotally connected means to move in an opposite direction, and a snubber arranged to engage said arm to cushion the movement of said pivotally connected means during its movement in the last named direction.

5. In a control mechanism, the combination of, fluid responsive means, linkage means for controlling a flow of fluid, said linkage means being arranged to be contacted and moved in one direction by said fluid responsive means after a predetermined travel thereof, an arm rigid with said linkage means, means carried by said linkage means, latch means arranged to engage said carried means for maintaining said linkage means in a predetermined position, means adapted to be engaged by said linkage means upon nearing the limit of its travel in one direction for causing said fluid responsive means to return to its normal position, means for disengaging said latch means from said carried means, and a resilient means within the path of said arm for snubbing the action of said linkage means during its movement in an opposite direction.

6. In a control mechanism, the combination of, a fluid responsive means, reciprocating means associated with said fluid responsive means, linkage means arranged to be raised only by said reciprocating means, means carried by said linkage means, selectively controlled means arranged to contact said carried means for maintaining said linkage means in a predetermined position, said carried means being adjustable to determine the movement of said linkage means, and means adapted to be actuated by one of said previously named means upon nearing the limit of its travel in one direction for causing the drainage of fluid pressure from said fluid responsive means and permitting said reciprocating means to be lowered.

BERTRAND J APIKSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED sTATEs PATENTS 

